The present invention relates to conversion of digital data between different formats, and more particularly to a format converter architecture for converting an incoming analog signal having an orthogonal structure, such as television video from different video sources having different television formats, to a pre-existing digital format for storage on a digital video tape recorder (DVTR) or for other processing by equipment built for use with the pre-existing digital format, and also for automatically converting the digital data in the pre-existing digital format back to the format of the original incoming analog signal.
As is well known there are many different kinds of video signal formats proposed or in general use throughout the world in both graphics and television equipment. Generally signal processing and recording equipment must be designed for a specific signal format. The cost and effort associated with the design of this equipment is considerable, inhibiting the development of newer and perhaps more appropriate signal formats for video image signals.
Currently there is a discussion in the television community as to what video signal format should be adopted by the United States for high definition television (HDTV). The formats being considered include a 525/59.94/1:1 format, a 1050/59.94/2:1 format, a (787+788)/59.94/1:1 format, and a 1125/59.94/2:1 format. There presently exists equipment that is compatible with the 1125 format, such as a digital video tape recorder (DVTR) manufactured by Sony Corporation of Tokyo, Japan. To provide a comparison between these various formats it is desirable to be able to record the video from sources representing each of the proposed video formats onto a single video tape recorder, and then to be able to play back the signals from the video tape recorder in their original formats.
One architecture for a format converter design has been proposed by the Advanced Television Test Center (ATTC) located in Alexandria, Va., and is disclosed in U.S. patent application Ser. No. 07/409,190 filed Sep. 7, 1989 by Charles W. Rhodes entitled "Multiple HDTV Format Digital Signal Converter." This architecture converts input video signals having one video format into the video format of a specific DVTR, such as the Sony recorder referred to above. The input video signal is digitized, using the horizontal and vertical drive synchronizing signals derived from the input signal, and stored in a buffer memory at the input signal sample rate. The stored digitized signal is then read out of the memory at the rate of operation of the DVTR. During playback the data from the DVTR is stored in the memory at the DVTR rate and read out to a digital-to-analog converter at the original sample rate. A pair of dummy samples is inserted in each line of the input signal data so that the input video lines provide a repeating pattern every seven or fourteen lines. This repetitive pattern is provided so that memory size may be minimized. The dummy samples may contain information such as parity bits, synchronization bits, memory row identifier bits, a frame start identifier bit, or the like. Unfortunately the Rhodes' format converter does not take into consideration the fact that the number of active video lines in each of the two fields in the 1125/59.94/2:1 format used by the Sony DVTR are not equal. Also knowledge by the operator of the original format is necessary when converting from the DVTR format.
What is desired is a format converter architecture that provides a means of using pre-existing digital processing and record/playback equipment in conjunction with signal formats for which the equipment was not specifically designed in order to facilitate the introduction and comparative analysis of new signal formats, including encoding an input signal from a signal source into the digital format of the pre-existing video equipment and automatically decoding the digital signal from the pre-existing video equipment back into the original format of the input signal.